I need new tires i have 245's and dont like the look as they are too small looking. 265's look better but i pull a 10000 lb 5vr and also enjoy 20-22 mpg on the road empty which i enjoy i only pull 5vr every other weekend usually short hauls, flat ground. Would 265's hurt preformance and milage Anybody else gone thru this same issue that can chime in with difference on mpg and power, Mostly mpg as i cant think there would be much noticeable power difference as it has so much torque, I have read a few times of 2-3 mpg drop by going from 245's to 265's; Wow is that real ??? My truck 06 lbz all stock. Thanks

My truck is all stock like yours and within 10k miles except it's 4x4 and has 265 Uniroyal's on the stock pizza cutter wheels. The only mod I have done is opening up the factory air box. I have a cat and muffler and I average ~15.5 mpg every fill-up. I get better on the highway but even at just running 65 mph, I will not break 18mpg.
I drive my truck like a grandpa most of the time shifting around 2k rpm's. My driving can be classified as 30% highway and 70% stop and go/55-60 mph roads/city driving.
Hope that helps.
I'm actually thinking of going down to 245's to try and squeeze a mpg or two more but man I hate the look of these stock pizza cutters. It's not that their ugly by any means but they just don't fit on such a large truck.

Well a 265 may weight more depending on what type and ply you get. They are bigger and through of the speedometer a bit so unless you correct for that it will difficult to figure mileage unless you take that in your calculation. So pretty much if looking at 265 comparable tire it is bigger and heavier. More rolling mass to get going. I probably lost almost 1mpg on a 2300 2500 Avalanche with and 8.1L gasser when changing tires from 245 to 265.

Brian

Think of it this way, the 06 2500 came with 245's while the 3500 single rear wheel trucks came with 265's. Same brakes, same drive ratios, same engine and trans. My 3500 SRW gets comprable mileage, slightly less but not a lot. If you get the larger tires, you will need to get your speedometer recalibrated. Tuners can do this, as can the dealer, if you can convince them to do so.

One thing though, your rims are .5" narrower. I don't think it means squat but some mfgs of 265s recommend 7" minimum and since yours are 6.5" the tire place might give some static.

I would get the 265's. You may lose a tad on the mileage, but it will look much better. Like Tom said the 3500 swr comes with a 265. I would check your speedo against a "known" accurate one before I made any changes. It may be close enough to call good. I run 305's on mine and have a "tuner" that can adjust the speedo. It seems to be very close with the factory settings to leave it alone. I have compared it with the little unmanned radar trailers the cops leave around to scare you. I am always pretty much dead on.